Pulpstone



June 10, 1947. w. 1.. HOWE El'AL 2,421,335

PULPSTONE Filed Sept. 18, 1945 2 Shets-Sheet 1 .26 [2 [0 I4 I 26 10 I2 15 /4 I l5 l2 l6 0 [2 IO 16 14 I l4 l5 3 22 23 3mm l4 23a 21a WALL/413g LrHUWE' LURENzp 5.WA5HBLIRN June 10, 1947. w, H E ETAL 2,421,885

PULPS'I'ONE Filed Sept. 18, 1945 2 Sheets-Sheet 2 WALLACE I HUWE LURENZU 5. WA'EHBLJRN Patented June 10, 1947 PULPSTONE Wallace L. Howe, West Boylston, and Lorenzo S.

Washburn, Worcester, Mass, assignors to Norton Company, Worcester, Mass, a corporation of Massachusetts Application September 18, 1945, Serial No. 616,984

6 Claims.

The invention relates to pulpstones, and with regard to its more specific features, to improved means for securing abrasive blocks to a central support.

One object of the invention is to provide a stronger pulpstone. Another object of the invention is to increase substantially the breaking strength of the union between the abrasive blocks and the central support. Another object of the invention is to eliminate or reduce cracking of the blocks on account of differential expansion of the blocks and the central support.

Another object of the invention is to provide a pulpstone construction which issimpler to manufacture than prior constructions. Another object of the invention is to improve the pulpstone described in U. S. Letters Patent No. 2,141,608 to Thure Larsson, and also the pulpstones of the patents referred to therein. Other objects will be in part obvious or in part pointed out hereinafter.

The invention accordingly consists in the features of construction, combinations of elements, arrangements of parts, and in the several steps and relation and order of each of said steps to one or more of the others thereof, all as will be illustratively described herein, and the scope of the application of which will be indicated in the following claims.

In the accompanying drawings illustrating two of many possible embodiments of the mechanical features of the invention,

Figure 1 is a fragmentary sectional view of a pulpstone constructed in accordance with the invention;

Figure 2 is an enlarged elevation of a holding bolt for the attachment of the blocks to the center;

Figure 3 is a sectional diagrammatic view i1- lustrating a feature of the invention; and

Figure 4 is a fragmentary sectional View of a pulpstone, showing a modification of the invention.

Referring first to Figure l, we provide a number of blocks ll] of bonded abrasive material. Each block H] is composed of any desired type of abrasive, such as quartz, silicon carbide or fused alumina, the latter two being preferred, bonded together with suitable bonding material, vitrified ceramic bond being preferred. Each block is preferably formed from a mixture of clay or frit with abrasive, suitably plasticized as by the provision of a suitable amount of plastic clay and the addition of water, then molded in a suitable mold and pressed under high pressure to cause the block to have suflicient green strength for handling.

In any suitable manner we form threaded holes in the blocks 10 complementary to the threaded ends 1 2 of holding bolts 13. Referring now especially to Figure 2, the threaded ends l2 of the bolts l3 have large rounded threads l4 leaving large rounded grooves 15 between convolutions of the threads. These grooves 15, and consequently the threads 15 of abrasive material which fit therein, are preferably somewhat larger than the metal threads 14; in an illustrative embodiment of the invention the grooves 15 have a radius of .135 inch, while the metal threads I 4 have a radius of .115 inch. In a particular embodiment of the invention the pitch of a thread I4 is .5

' inch, and a threaded end I2 is 2.25 inches long.

For the formation of the threaded holes in the blocks [0 we may provide metal cores (preferably of hardened steel) having threads and grooves of the same shapes as the threads I 4 and grooves 15, but these cores are longer than the threaded ends I! and they are slightly larger in diameter, for example, of the order of .025 inch larger in overall diameter. Such cores extend through correspondingly threaded holes in the bottom mold plate of the mold for manufacturing the blocks H), and the abrasive mixture is molded and pressed around them. Each such core has same means for turning it, for example, a screw driver slot in the outer end, and after the mixture is pressed the cores are screwed out of the holes which they have formed in the green block. Unscrewing of the cores is preferably done after all parts have been stripped from the green block except the bottom plate.

It is somewhat surprising that a threaded hole having a strong thread of dense abrasive, and to the desired size and shape within close limits, may be thus formed, since it was feared that the abrasive bond mixture would not flow well into the reentrant portions of the core represented by the abrasive thread 16, but satisfactory results have been achieved in actual practice. Other manners of forming the threaded holes are considered less practical, since drilling and thread- '5 ing a vitrified block would be prohibitively costly, while accurately threading a hole in the green block would be diflicult.

After blocks l0 are formed as thus described, and after reentrant grooves 20 are formed (by shaving) at the corners, as mentioned in the aforementioned Patent No. 2,141,608, the blocks [0 are fired in a kiln and the material is thereby converted to vitrified bonded abrasive material, and the shape is permanent.

Referring to the embodiment of Figure 2, the bolts 13 have large diameter portions 2! which may be one inch in diameter, with conical or bevelled sides 22, separated by small diameter portions 23, which may be of .75 inch diameter. The portions 2| and 22 thus constitute integral rings with bevelled sides. There may be, as shown, eight of such rings. In the drawings seven of these rings are shown to have the same shape while the ring 2 la is slightly narrower and is connected to the threaded portion I2 by a reduced portion 23a of somewhat greater diameter than the portions 23, but such features in? cluding the number of rings may be varied without departing from the invention.

In order that bolts l3 may firmly and tightly hold the blocks without any lost motion or play, we provide a suitable cement. We have found that an excellent cement for this purpose is phenol-formaldehyde A stage resin plasticized to the consistency of a heavy cream by means of liquid furfural. The threaded holes in the blocks H] are first filled with this cement which is then poured off. The cement penetrates some distance into the abrasive, sealing the holes against admittance of pulp water when the stone is used. Furthermore, the cement strengthens the abrasive thread l6. After the cement in the threaded holes has been air dried, some more cement is brushed onto the threaded ends l2 of the bolts l3 and they are then screwed into the blocks ID to the position shown in Fig. 1. We may use other cements, such as semi-hard rubber, vulcanizedin situ, or a self-curing resinous mixture, copper oxide cement, or a watery mixture of Portland cement. There are preferably four bolts l3 for each block 10, the spacing arrangement being preferably the same as indicated in the patent to Larsson, No. 2,141,608.

The blocks ID are then built up into a cylinder, a suitable filler material 26 such as described in Larsson Patent No. 2,054,771 being placed between the blocks. We use any temporary holding members such as circumferential clamps to hold the blocks together as built up and then place the entire structure thus formed in an oven where it is heated to cure the phenol-formaldehyde-furfural resin and to vulcanize the rubber of the filler material 26 in accordance with the Larsson Patent No. 2,054,771. A suitable heat treatment is 24 hours at an oven temperature of 160 C. The phenol is cross-linked by the formaldehyde and the furfural and the cement is thus set to a hard "0 stage resin by such heat treatment.

We now remove the built-up cylinder from the oven and place inside of it a plurality of steel reinforcing hoops 30 suitably wired together and forming in effect a plurality of concentric cages. We provide a two-part metal drum which we place within the above cages also concentric with the cages and the built-up cylinder of blocks In. The bolts l3 extend between successive levels of the outer hoops 30. We then pour concrete 32 in position between the central metal drum and the blocks I0 and allow it to set. The metal clamps and the central metal drum (which is in two parts each tapered toward the center) may now be removed and the stone is now substantially complete, except for features of construction relating to the mounting, which need not herein be described.

The portions 2| and 22 which are integral rings with bevelled sides are embedded in the concrete which is interlocked with the small diameter portions 23 and it has been found that thereby the bolts are securely held to the concrete.

The bolts l3 may be made of any strong nonbrittle metal, preferably a ferrous metal. Ordinary cold rolled steel would be satisfactory, but turning of the threaded end l2 and the portions (grooves) 23 is expensive and a typical pulpstone has 400 of such bolts. We prefer to use a pearlite malleable iron of which Z metal is a good example. This can be cast, and after heat treatment, the threaded end I2 is ground to remove the casting fins and to shape it within the required tolerances. The part of the bolt l3 which is to be embedded in the concrete, however, may be left rough.

This Z metal and other pearlite malleable irons have low coefiicients of expansion, of the order of .0000066 which differs only slightly from concrete which is of the order of .0000060 (both on the Fahrenheit scale). Vitrified abrasive has a coeflicient ranging from about .0000025 to .0000040.

Referring now to Figure 3, it will be seen that a thread l4, when the bolt I3 i in tension as by the centrifugal force of the block l0, exerts a compression force which is transmitted along columns 40 indicated roughly by the dotted lines in Figure 3. The compression is thus spread over a large section of the abrasive block and this has been shown by pull tests wherein the holding power of the bolt l3 in the block [0 was tested to destruction. The bolt did not break nor did it pull out of the block ill but rather a large frustoconical section of the abrasive block In broke off. The entire area roughly outlined by the columns of compression 40 was pulled from the block 10.

A number of such tests to destruction were made and breakage was at 18,000 lbs., to 24,000 lbs. On the other hand, a bolt of the type illustrated in the patent to Larsson, No. 2,141,608, wherein the head of the bolt is embedded in Portland cement and iron fillings in the hole in the abrasive block, pulled right out of the block, breaking the cement. A number of tests were made on the holding power of such bolts in the blocks and breakage was at 10,000 to 15,000 lbs. in the several tests.

Ordinary stresses and centrifugal force will not cause any breakage of pulpstones constructed in accordance with the Larsson Patent 2,141,608. Pulpstones constructed in accordance with that Larsson patent have given excellent results in actual service for many years. However, in the life of any pulpstone there is apt to come a day when something goes wrong with the grinder, for example, the supply of water is suddenly cut off, and then the abrasive blocks [0 rapidly heat up and reach a high temperature before the heat can penetrate to the concrete core. The filler material 26 which likewise was used in the pulpstone of the Larsson Patent 2,141,608 takes care of circumferential expansion and prevents that from causing the blocks as a whole to draw away from the concrete center. It was thought that, provision having thus been made to prevent expansive force from causing a radial resultant by circumferential expansion, the blocks would no longer come out. Nevertheless breakage still oc casionally occurred at the cement filled holes,

that is, where the bolts of the Larsson patent are 5 embedded in the abrasive blocks. This breakage has increased in recent years because the pulp manufacturers have been running the stones at higher speeds and using greater pressures.

As a result of the use of the bolts of the present invention secured to the abrasive blocks II] in the manner described, breakage of pulpstones has been reduced. The present construction is considerably stronger than that of the Larsson Patent No. 2,141,608, and at the point where the structure of the Larsson patent was weakest. The pulpstone of the invention is able to withstand the higher speeds and pressures now used.

Referring now to Figure 4, what we believe to be a still further improvement is therein illustrated in a modification of the invention. A bolt l3a has a threaded end l2 like the threaded ends l2 of the bolts [3 and it likewise has large diameter portions 2| with conical or bevelled sides 22 separated by small diameter portions 23. However, a pair of such large diameter portions, namely, the ring 2Ia and an adjacent integral ring 2|, are omitted and a portion 23b of uniform cross-section is substituted. Around this portion 23b is wound a piece of cardboard or heavy paper 4| of the order of .010 inch thick. We may also use other materials, such as rubber. Such materials are deformable. We may also coat this portion with a substance which will melt and flow into the concrete when the stone is heated in use. Paraffine is an example. The purpose of such materials is to keep the rigid concrete away from the bolt at this locus. The construction is otherwise as described in the case of the embodiment of Figure 1.

In the case of the embodiment of Figure 4, the portions of uniform cross-section 2312 are capable of moving slightly in the concrete by bending of such portions 23b and compression of the paper, or because there is a void in the concrete at this locus. Thus differential expansion between the blocks l0 and the concrete center 32 is permitted without cracking the stone. Such differential expansion (including contraction) otherwise sets up a shearing force upon the bolts l3 by reason of the fact that the concrete phase changes" abruptly to the abrasive phase.

The threads of abrasive material [6 are strong because they ar rounded and of generous size. Furthermore, by rounding the threads IS, the threads Hi, the grooves I 5, and the grooves in the abrasive material, difficulty in screwing the bolts I3 into the blocks I0 after the blocks have been vitrified is eliminated. The threads l6 should have a radius of no less than .020 inch, that is, a diameter of no less than .040 inch.

However, we are not limited to rounded threads, since square or V-shaped threads may be used. The V thread may have an angle of 60 degrees or a different angle. Nevertheless, such threads should also preferably be of generous size, and the thread in the abrasive should preferably be of no less size. If a square thread is used, the width of the thread should be no less than .040 inch. If a V thread is used, the width half way from the base to the top should be no less than .040 inch. If in each case the corresponding dimension of the abrasive thread is no less than .040 inch, it follows that the pitch of the thread on the bolt is no less than .080 inch.

In this range, the smaller threads and pitches should only be used with blocks having abrasive of fine grit size.

The completed pulpstone is, a body of revolution the curved surface of which is the outer surfaces of a plurality of abrasive blocks. Usually such body of revolution will be a cylinder, but other surfaces such as spheroids, hyperboloids and paraboloids may be formed.

It will thus be seen that there has been provided by this invention a pulpstone and a method of manufacture thereof in which the various objects hereinabove set forth together with many thoroughly practical advantages are successfully achieved. As many possible embodiments may be made of the above invention and as many changes might be made in the embodiments above set forth, it is to be understood that all matter hereinbefore set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

We claim:

1. A pulpstone in the shape of a body of revolution the curved surface of which is the outer surfaces of a plurality of bonded abrasive blocks, comprising a plurality of said bonded abrasive blocks, a central concrete core, and a plurality of means each including a metal bolt to hold said ,blocks to said core, each of said means comprising a portion of varying cross-section of said bolt embedded in said concrete core, a thread on said bolt, a mating thread in a hole in said block the thread in the hole being of bonded abrasive material, and a layer of cement in the hole in said block and upon said threads, the pitch of the thread on the bolt being at least .080 inch.

2. A pulpstone in the shape of a body of revolution the curved surface of which is the outer surfaces of a plurality of bonded abrasive blocks, comprising a plurality of said bonded abrasive blocks, a central concrete core, and a plurality of means each including a metal bolt to hold said blocks to said core, each of said means comprising integral rings on said bolt embedded in said concrete core, a thread on said bolt, a mating thread in a hole in said block the thread in the hole being of bonded abrasive material, and a layer of cement in the hole in said block and upon said threads, the pitch of the thread on the bolt being at least .080 inch.

3. A pulpstone in the shape of a body of revolution the curved surface of which is the outer surfaces of a plurality of bonded abrasive blocks, comprising a plurality of said bonded abrasive blocks, a central concrete core, and a plurality of means each including a metal bolt to hold said blocks to said core, each of said means comprising a portion of varying cross-section of said bolt embedded in said concrete core, a thread on said bolt, a mating thread in a hole in said block the thread in the hole being of bonded abrasive material, and a layer of cement in the hole in said block and upon said threads.

4. A pulpstone in the shape of a body of revolution the curved surface of which is the outer surfaces of a plurality of bonded abrasive blocks, comprising a plurality of said bonded abrasive blocks, a central concrete core, and a plurality of means each including a metal bolt to hold said blocks to said core, each of said means comprising a portion of varying cross-section of said bolt embedded in said concrete core, a thread on said bolt, a mating thread in a hole in said block the thread in the hole being of bonded abrasive material, the pitch of the thread on the bolt being at least .080 inch. 7

5. A pulpstone in the shape of a body of revolutionthe curved surface of which is the outer surfaces of a plurality of bonded abrasive blocks, comprising a plurality of said bonded. abrasive blocks, a central concrete core, and a plurality of means each including a metal bolt to hold said blocks to said core, each of said means comprising a thread on said bolt, a mating thread in a hole in said block the thread in the hole being of bonded abrasive material, a portion of varying cross-section of said bolt embedded in said concrete, and a portion of uniform cross-section of said bolt in said concrete and extending between said block and said portion of varying cross-section, said concrete being spaced from said portion of uniform cross-section in directions radial thereof.

6. The method of making a pulpstone block by 20 means of a mold which comprises screwing a 8 threaded core through a mold plate to the inside of the mold, filling said mold with a mixture of abrasive and bonding material, pressing, then unscrewing the threaded core, and finally hardening the bonding material.

WALLACE L. HOWE. LORENZO s. WASHBURN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

